Pattern for piston-rings



A. 1' MUMMERT! PATTERN FOR PISTON RINGS, I APPLICATION FILED SEPT. 5 I919.

' 1,333,212, Patented Mar. 9, 1920.

2 SHEETSSHEET I.

e //v VENTOR. 1

A TTORNEX A. J. MUMMERT.

PATTERN'FOR PISTON RINGS, APPLICATION HLED SEPT. 5. l9l9.

1,333,2 1 2. Patented Mar. 9, 1920 2 SHEETS-SHEET 2.

lA/VE/VTDR.

Arden UNumm er!- 5 YM 21m UNITED, STATES PATENT OFFICE.

ARDEN J. -MUMMERT, OF ST. LOUIS, MISSOURI, ,ASSIGNOR TO McQUAY-NORRIS MANU- FACTURING COMPANY, A CORPORATION OF MISSOURI.

\ PATTERN FOR PISTON-RINGS Specification of Letters Patent.

Patented Mani), 1920.

Original application filed February 5, 1918, Serial No. 215,469. Divided and this application filed September 5, 1919. Serial No. 321,917.

' T all whom'z't may concern:

, Be it known that I, ARDEN J. MUMMERT,

St. Louis, State of Missouri, have invented certain new and useful Improvements in Patterns for Piston-Rings, of which the following is a full, clear, and exact description, reference being had to the accompanying drawings, forming a part hereof.

The present is a division of my pending application for improvements in the manufacture of packing rings for pistons, Serial Number 215,469, filed February 5-, 1918, being specifically directed to the pattern from which is cast the blank out of which the piston ring is made. The object sought is to provide a pattern so shaped as to produce a blank from which may be derived a. split or open piston ring of substantially uniform cross-section and so contoured that when the ring is inserted into the cylinder in which it is intended to operate, the same will not only conform to the circular cross-sec tion of the cylinder but will engage the walls thereof with uniform pressure throughout its entire circumference. In other words, the object sought is to rovide a pattern from which may be ultlmately derived a split metal piston ring that will be truly circular or round'while in service and that will exert at all points uniform radial pressure against the walls of the cylinder in which the same is confined. In this type of ring the contact with the cylinder walls is brought about by the outward spring of the metal of which the ring is composed, the radial pressure exerted against said walls depending on the shape of the ring when free (or out of the cylinder), on the crosssection of the ring, and on the resilience of the metal (or other material) from which the ring is made. The circumferential dimension of the ring should be sufficient to permit the ring when laced on its piston and deposited in the cylinder, to expand into or assume the formof an annular or circular body whoseouter face or periphery shall contact at all points with, and exert equal radial'pressure'against, the walls of the cyl-' inder. Rings of this character being usually cast, it necessarily follows that the resilience of the metal'can be availed of only by splitting or parting the ring and thereby leaving a gap which will permit of suificient contraction in the ring to impose on the metal the necessary tension under which it tends to resume its original expanded position, this tension being the force which acts radially'upon the walls of the cylinder when the contracted ring is inserted thereinto. As ordinarily constructed, a packing ring is made by cutting a circular blank or ring of iron of proper width and thickness from a tube casting, the outside diameter of the ring exceeding the diameter of the cylinder bore designed to receive it. This excess in diameter (by way of example) is approximately one thirty-second of an inch for every inch of diameter of the cylinder bore, so that if the diameter of the bore is four inches, the outside diameter of the ring would be four and four-thirty-seconds inches. The rule of the thickness of the ring is also one thirty-second of an inch thickness for each inch of diameter of bore, a cylinder four inches in diameter requiring a ring four thirty-seconds of an inchin thickness. From this oversize circular blank there is cut a segment, thereby leaving the necessary radial pressureagainst the walls of the cylinder, forming a joint there.- with, and preventing the escape of any fluid that is to be held by the piston. A ring made in the manner outlined above does not contact with the walls of the cylinder to the same degree at all points, owing to the distortion of the ring from a true 'clrcular form when contracted; and in practice the portions of the ring contiguous to the ends on each side of the gap are more or less 'outof contact so as to leave a clearance between the ring and cylinder walls and permit the gases or fluid to escape therethrough. In

this type of ring the greatest radial pressure will be found at the ends and at the mid section, the poorer contact and hence the less pressure being confined to the sec tions ninety (90) degrees from either of the oints of maximum pressure referred to. It is therefore apparent that a'piston ring to operate with uniform pressure in the cylinder must not .be a perfect circle when free,

and conversely if the proper initial curvature be imparted to the ring when free and not contracted or compressed, it will show a uniform pressure per square inch at every point of contact with the cylinder walls, when contracted. In the defective type of ring above alluded to, the error is often corrected by lapping or scraping the outer face of the ring so as to present a more uniform pressure throughout its entire periphery; but thispractice consumes time and labor and is for that reason objectionable. In the early stages of development of my invention I succeeded in securing uniform radial pressure throughout the entire circumference of a ring by bending a split circular ring at different sections from a very heavy curve at the ends to a very light one at the mid section. The general outline of the ring when free was no longer a true circle, but followed a curve taken from a templet. The templet curve was derived by calculating the stresses at diiferent sections of a hypothetical ring which was assumed to exert the same radial pressure per square inch at all points against the cylinder walls. It was found that these stresses decreased uniformly from the mid section to the ends of the ring, the curve being calculated to so vary the radii at different sections of the ring as to produce a ring which when free was not a true circle. Such a ring when compressed would produce the proper stress relations at different sections so as to exert substantially uniform radial pressure against the cylinder walls along its entire circumference. To bend each ring individually however, consumes time and labor,

to eliminate which is one of the objects of" my present improvement. I avail myself of the curvature of the templet based on the stress calculations of the hypothetical ring aforesaid, but in lieu of imparting this curvature to each individual split circular ring by the bending and straining process abovereferred to, I provide a suitable pattern from which is cast the blank from which the finished piston ring is directly made. The method by which the pattern for this blank is obtained, as well as the pattern and resulting blank and finished ring I consider to be new. The advantages of the invention will be fully apparent from the following detailed description in connection with the accompanying drawings in which- Figure 1 represents a plan of the closed pattern ring employed at-the initial stage of my invention, said ring exceeding in outside diameter the diameter of the cylinder bore designed to receive it, the bore being shown dotted; Fig. 2 is a plan of the same-ring showing the initial saw slot or cut therein, the cylinder bore being .dotted; Fig. 3 is a plan of the slit ring shown superposed over the circle defining the bore of the cylinder,

the dotted lines representing the deflection to which the ends of the ring are subjected and the distortion from a true circle suffered by the ring in consequence; Fig. 4 is a plan of the distorted ring with the bore line shown dotted; Fig. 5 is a plan of the distorted ring with the saw slot or cut closed by a suitable filler and serving as a pattern;

Referring to the drawings, 3 represents the o'ri 'nal pattern ring as cut from an iron tu e casting, the outer diameter of which exceeds that of the cylinder bore B as previously pointed out. The next step in the operation is to cut a slit :5 across the ring with a fine saw thereby splitting or parting the ring as shown. The portions of the ring on each side of the slit are next bent into non-circular form by forcing the same inwardly or radially toward the center of the ring, the free ends thereof under the bending operation being displaced or forced from their original position a. distance which, though necessarily varying with the character of the material used, in the present example amounts to substantially one-half the thickness of the ring, this bending action operating to-distort the ring into a form or pattern 3' shown by the dotted lines in Fig. 3, and as shown in Figs. 4 and 5. The displacement and distortion are effected in any mechanical manner, but preferably by a machine which gradually strains or bends each section of the ring from the mid section m (the portion diametrically opposite the slit t) to the ends of thering. The greatest bending is produced in the portions or sections of the ring nearest the ends, the bending or displacement decreasing as we approach the mid section. Thus, assuming (Fig. 5) the point at to represent the geometric center of the ring before distortion, it will be seen' that the curvatures of the outer faces of the distorted portions follow, or are defined by, the outer terminals of radii vectors, 1', r, 'r", r', 1, progressively decreasing in length from the ends e, e, of the mid section m, the outside radius of .curvature R of which corresponds substantially to the radius of curvature of the outer face of the ring 3 before distortion. The slit t in the pattern 3 is preferably (though not necessarily) closed by a filler h of wax, solder, copper or other material as shown in Fig. 5, the presence of the filler insuring a more rigid pattern. With this distorted ring 3 as a pattern I cast the ring-blank 3" displacement of the free ends of the slit ring 3, that is to say,.the length of the segment removed is in the ratio of the circumference to the radius along which the displacement was made. By removing the segment u We finally obtain an open ring 4. with a gap 0 as shown in Fig. 8, sucha ring when contracted (and finished) and inserted in the cylinder Ci contacting with the cylinder walls and exerting even pressure against said walls throughout its entire periphery. and making a tight joint with said walls.

In the present example, the distortion suffered by the slit ring 3 under the bending operation resulted in a radial displacement of the terminals of the ring of substantially one-half the thickness of the ring; the length of the segment u removed from the distorted ring blank 3'5 was equal substan: tially to six times this radial displacement; the thickness of the ring was given as corresponding substantially" to onethirty-second of an inch for each inch diameter of the cyl inder bore; the excess of the outside diame: ter of the original or pattern ring 3 over the diameter of the cylinder was given as one thirty-second of an inch for each inch diameter of-the cylinder. These various di-' menslons and relat ons, 1t is to be understood are here given by way of example because frequently occurring in practice; but the same may be departed from by those skilled in the art according to the conditions to be met. Much depends on the molecular structure of the metal from which the ring blank 3 is-cast; much on the limit of elasticity of the metal; much on the cross-sec-' tional area of the ring; on'the resilience of the metal, and on other considerations tobe taken into account as they present themselves to the skilled mechanic.

The outside radius of curvature R of the mid section m of the pattern 3 corresponds substantially to the radius of curvature of the outer face of the ring 3 before distor} tion, that is to say, it is a radius larger, than the radius'of-curvature of the bore B of the cylinder in whichthe ring is to .operate.

This radius of curvature progressively diminishes from the midsection m'to, a point diametrically opposite the center 'of said section as apparent fromthe progressively diminishing radii vectors 1", r, r", r, r the shortest radius vector 1 terminating at the outside of the slit t or the filler h closing the same, as shown. The shortest radius vector 1"" should preferably be a shade less than the radius of curvature of the bore of the cylinder, thereby leaving-the radii vectors which lead to the points corresponding to the ends of the outer curve .of the segment a removed fromthe blank 3 substantially equal to the radius of'curvature of the cylinder bore. We thus produce a pattern (Figs. 4, 5,) having on one side a portion or mid sectionmt whose outside radius of curvature is inexcess of'the radius of curvature of the bore of the cylinder in which the ring is to operate, the radii=(vectors) decreasing in bothdirections from said mid section until they attain a length substantially equal to the radius of 'curvature of the cylinder 'bore'at points corresponding to the ends of the outer curve of the segment it removed from the blank 3 cast from said pattern. As previously stated such a pattern and method of producing the same, as well as the ring-blank (3 cast therefrom and the finished ring (4) I consider to be new.

It will be seen from Fig. which the;

cylinder bore is represented by the dotted line B, that the radial displacement of the ends of the ring 3 in the process'of distortion to form the pattern 3 is suflicient-to obtained falling within the spirit of my invention. 'It was stated at the outset that a piston ring exertin uniform radlal pressure against the cy mder walls throughout its entire circumferencemay be formed by the proper bending and distortion of an original split circular ring, the curvature of the distorted ring being taken from a templet. Such a ring may approach or actually conform to the curvature .of the cast ring 4: under my present invention, but besides being open to the objections heretofore 'pointed out .(theconsumption of time and labor) it is open to the further objection that its fibers and molecules have been strained in the distorting rocess, this straining in a measure detracting from the elasticity and resilience of the ring- By my present method I secure a ring 4 of proper contour by casting; and since its molecules have not been disturbed by distortion and bending to bring it into the desired shape, it

follows that its elasticity and resilience have not in any wise been impaired or affected.

Such a ring (see Fig. 8) comprises a mid section m whose outer radius of curvature is in excess of the radius of curvature of the bore of the cylinder in which the ring is to operate, conforming in the main to that of and while so contracted the same is ground the original pattern ring 3, and non-circular side sections 8, 8, whose outer curvatures follow the terminals of, radii vectors progressively diminishing in length from said mid section toward the gap 0 at which gap they correspond substantially to the radius of curvature of the cylinder bore. These curvatures are eccentric and interior to the outer circle 6 representing the curvature of the outer face of the original pattern ring 3, and in the main exterior and eccentric to the 'bore line B. It is to be understood that I do not wish to be limited to the precise relation in the lengths between the radius of the cylinder bore and the shortest radius vector defining the maximum displacement of the ring terminals. A ring in which the shortest radius vector exceeded in length the radius of the cylinder bore would likewise fall within the spirit of my invention.

The gap 0 of course is sufficient to permit the ring to be contracted to a perfectly circular form and to a dimension to permit insertion of the contracted rin into the cylinder G having the bore B. t' may be stated in passing that the curve imparted to the slit ring 3 to form the pattern 3 is taken froma templet the curve of which is derived by calculating the stresses at different sections of a hypothetical ring exerting, or assumed to exert, a uniform radial pressure per square inch at all points against the cylinder walls. This templet curve maybe imparted to individual split circular piston rings as heretofore described, but as already pointed out this method is laborious, slow, and ex-' ensive, and impairs the resilience of the mshed ring. It is of course necessary be fore the ring is put to use that the same be ground or finished to remove surface irregularities so as to obtain a perfectly cylindrical and smooth bearing surface for the ring when inserted into the cylinder. To grind the ring the same is held contracted or'compressed in a suitable jig or machine,

and finished to the proper working conditions. The ring thus finished will be perfectly round and true and exert uniform radial pressure at all points against the walls of the cylinder in which it 1s to operate. -For convenience we may assume the ring 4 to have been ground previous to its use of the filler h closing the saw slot. \Vith the filler it however we secure a somewhat stiffer pattern. It is apparent of course that I may cut .out or remove a segment such as u from the pattern 3 (if made of the proper metal) and secure a piston ring on the order of that herein contemplated, such an alter native falling within the scope of the resent invention. But, as pointed out a ve, this method is not desired in practice involvin as it does the individual bending and distortion of each ring, and resulting in a measure in the straining of the fibers from their original condition and reducing the elasticit of the ring. It may be stated in passing that when a circular ring such as 3 is slit and subjected to the distortion here described, to produce the pattern 3, the outside radius of curvature R theoretically begins to shorten or decrease in'length from a point diametrically opposite the slit t, so

that at this point only does the radius re.

main its full original length. Practically however the shortening of the radii is not perceptible until the points 6, e, are reached, the positions of these points depending of course on the diameter of the ring, the material employed, thecross-section of the ring and like factors not necessary to mention.

h of the inside radius of curvature of the ring is controlled in substantially the same way. It is to be understood therefore that what is herein referredto as the midsection .of the ring, is that portion oppo- The lengt site the slit t or gap 0 whose outside radius of curvatureremains practically constant and substantially of the length of the radius It of the ring before distortion, no fixed length for said mid-section being claimed or urged herein. In bending the slit circular riiig 3 shown in Figs. 2 and 3 into the distorted or non-circular form 3' indi cated by the dotted lines in Fig. 3, and as shown-1n Figs. 4 and 5, the slit t contracts somewhat, but the amount is so slight that in order to bring it out, the original width of the slit is purposely exa' gerated in Figs. 2 and 3, the contraction 0 early appearing inthe somewhat narrower dotted line slit in Fig. 3, and Fig. 4. g

Having described my inventlon what I claim is:. i

1. A pattern for piston rings, comprising in the slit of the ring shown in exceeds the radius'of curvature of the cylinder in which the piston ring derived from the blank cast from said pattern is to operate, said portion being bounded by non-circular portions the outer curvatures iof which follow the terminals of radii vectorsprogres sively decreasing in length from the ends of a ring having on one side a curved portiorm or section whose outside radius of curvature the first named portion to a point opposite said portion.

2. A pattern for piston rings, comprising,

a ring having a mid section whose outside radius of curvature exceeds the radius of curvature of the cylinder in which the piston ring derived from the blank cast from the pattern is to operate, said mid section being bounded by non-circular sections meeting at a point opposite the center of the mid section, the curvatures of the outer faces of said bounding sections following the outer terminals of radii vectors leading fromthe center of the are defining the outside curvature of the mid section, said radii vectors progressively decreasing in length from the ends of the mid section to the meeting point of the bounding sections.

3. A pattern for piston rings, comprising a ring having a mid section whose outside radius of curvature exceeds the radius of curvature of the cylinder in which the piston ring derived from the blank cast from the pattern is to operate, said mid section being bounded by non-circular sections terminating at a point opposite the center of the mid section, the outside curvatures of said bounding sections following the outer terminals of radii vectors leading from the center of the are defining the outside curvature of the mid section, said radii vectors being shorter than the outside radius of curvature of the mid section and progressively decreasing in length from the ends of the mid section to the meeting point of the bounding sections.

4. A pattern for a split metal piston ring, comprising a ring having a mid section whose outside radius of curvature exceeds the radius of curvature of the cylinder in which the piston ring derived from the blank cast from the pattern is to operate, said mid section being bounded by non-circular sections terminatin at a point opposite the center of the mid section, the outside curvatures of said bounding sections following the outer terminals of radii vectors leading from the center of the arc defining the outside curvature of the mid section, said radii vectors being shorter than the outside radius of curvatureof the mid section and progressively decreasing in length from the ends of the mid section to the meeting point of the bounding sections, the portion of the pattern disposed on oppositesides of the meeting point aforesaid and corresponding to the section removed from the blank cast from the pattern being bounded by radii vectors corresponding in length substantially to the radius of the bore of the cylinder in which the piston ring is to operate.

5. A pattern for a split metal piston ring,

larger than working size, the radial dimensions increasing progressively from the ends of the ring to the mid section, but is round when compressed to said working size, consisting of a non-circular ring comprising a portion having the shape assumed by th split metal piston ring when free.

6. A pattern for a split metal piston ring, which piston ring when free is radially larger than working size, the radial dimensions increasing progressively from the ends of the ring to the mid section but is round when compressed to said Working size, consisting of a continuous non-circular ring comprising a portion having the shape assumed by the split metal piston ring when free.

In testimony whereof I affix my signature in presence of two witnesses.

ARDEN J. MUMMERT.

Witnesses:

EMIL STAREK, PAUL R. DOLVIN. 

